Exposure Tactics • Color Control

What comes after using an incident meter to set the exposure? Setting a neutral color balance then refining the exposure, both in post production. I always refine the exposure after neutralizing the color. Before going into the steps for either one, here’s some background on digital captures, especially RAW files. (You are shooting RAW aren’t you?)
RAW captures have a huge amount of information in them. Half of that info is in the brightest f/stop of exposure as shown in the graphic below. There are 8192 tones in that first stop compared to 256 tones in an entire JPEG. A 14bit RAW file has about sixty-three times more information to work with than a JPEG of the same subject. That extra data provides the headroom for creative enhancements in the RAW processor before ever generating pixels for editing in Photoshop.

A 14-bit RAW file captures 63 times more data shooting an 8-bit JPEG.

RAW data is linear. There is no gamma curve imposed on the file as is the case in a JPEG capture. No curve means that colors won’t shift and contrast won’t increase either. Both happen to JPEGs when making big changes in exposure or color. The 2.2 gamma curve is necessary to distribute tonality so that it reads correctly to our eyes. Compare it to the linear version where the highlight data is expanded and the shadows are compressed.

The linear gamma of a RAW capture allows for large changes without building contrast or shifting

Commercial photography for advertising, catalog and e-commerce sites must be color accurate. By that I mean the highlights, midtones and shadows want to be as close to neutral as possible. Neutrality in this case means no color cast. Colors are neutral when the white, gray and black swatches on an X-Rite ColorChecker target, read the same values for the Red, Green & Blue channels. ColorChecker targets are colorimetrically neutral. That’s one reason they are a bit pricy and priceless at the same time. If the patches are protected from fingerprints, and when not in use, kept in a dark envelope, they will last many years. Below, model Jennie Carroll is holding the ColorChecker Passport. It’s a target in a durable plastic case. The file is open in Camera Raw 8.4.

A RAW file open in Camera Raw 8.4 shows the color values for white, middle gray and black before it is white balanced.

The white patch (#1 sampler) reads R:243, G:244, B:240, the middle gray (#2 sampler) is: R:138, G:140, B:132 and the black (#3 sampler) shows: R:37, G:37, B:36. In each instance, the red and green are brighter than the blue. The color cast is slightly yellow.
After correction the numbers are much closer to neutral. #1 now is R:243, G:243, B:242, #2 now reads R:138, G:137, B:138 and #3 shows R:38, G:38, B:39. The White Balance tool was clicked on the patch immediately below the #1 sampler to neutralize the photograph. Their numbers, R:226, G:226, B:226; are the same and completely neutral. A one point difference on the other patches will be more than close enough for all but he most hyper critical color outputs. There are tools in Photoshop that can make the numbers match perfectly. The difference in the example is subtle and noticeable.

Compare the neutralized version on the right to the one out of the camera on the left that is a bit yellow.

The corrected version is on the right. Camera Raw 8.4 is the first version that has before | after comparisons in the preview window. Press Q to cycle the preview modes. The “after” on the right shows three color samplers circled in red: #1 on the white patch, #2 on middle gray and #3 on the black patch. The corresponding readouts are shown in the red box at the upper left of the dialog. The next Exposure Tactics post shows how to tweak the exposure in post production.

Photography is life. Kevin is living it to the fullest. His practice includes fashion, editorial, architectural and corporate photography. Most of all he loves making photographs! Read his blogs here and at www.kevinamesphotography.com.

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8-bit usually refers to 8-bits-per-pixel-component (so R+G+B = 24 bits). An 8-bit JPEG has more than 16 Million colors (2^24), and around 11 stops of tonality, even though there are only 256 tones per pixel component.

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[…] To achieve a “proper” exposure start with color corrected photo. How is covered in a previous Exposure Tactics post. Since most RAW data is in the brightest f/stop of an exposure, highlights are the basis for […]

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